1. Field of the Invention
The present invention relates to a DC power supply circuit arrangement, and more particularly to an arrangement of an energy absorber used in a DC circuit breaker.
2. Description of the Related Art
A conventional DC power supply circuit composed of commutation type DC circuit breakers is disclosed in Japanese Patent Unexamined Publication JP-A-54-113038. As apparent from the Publication, energy absorbers are connected in parallel with respective circuit breakers. This arrangement is now described with reference to FIG. 3.
FIG. 3 is a circuit diagram showing part of a DC power supply circuit for a feeder used in an electric railway. A common conductor 1 is connected at its one side through circuit breakers 2A to 2C and AC-to-DC converting rectifiers 3A to 3C to a three-phase AC power source (not shown) and connected at its other side to switches 4A to 4E. The switches 4A to 4E, which may be unidirectional semiconductor switches through which a current can flow only in the direction of arrow, are connected in parallel with energy absorbers 6A to 6E formed of a non-linear resistor or a condenser. Output ends of the switches 4A and 4C are connected to an M-route feeder 30 and output ends of the switches 4B and 4D are connected to an N-route feeder 32 to supply DC power to electric trains or trolley cars through trolley lines in the respective routes.
In the DC power supply circuit, at least one of three circuit breakers 2 is always closed and a DC current flows in the direction of arrow shown by broken line.
If a short-circuit occurs at point A marked with X when one of circuit breakers 2 is closed, a short-circuit current i.sub.1 flows through the switch 4A. This short-circuit current is detected by a current transformer (not shown) and the switch 4A is opened to commutate the short-circuit current i.sub.1 to the energy absorber 6A. When the short-circuit current is commutated to the energy absorber 6, electric energy is converted into thermal energy to cut off the short-circuit current if the energy absorber is formed of, for example, a non-linear resistor.
Further, if a short-circuit occurs at a point B when a DC current i.sub.2 is supplied from an adjacent transformer substation (not shown) through the feeder 32, a short-circuit current flows from the adjacent substation through the feeder 32 and the switch 4E to the point B. When the short-circuit current is detected by a current transformer (not shown) and the switch 4E is opened, the short-circuit current is commutated to the energy absorber 6E and cut off in the same manner as above.
In the DC power supply circuit, however, each of the switches 4A to 4E requires one energy absorber and accordingly the DC power supply circuit is not only large in structure but also expensive.